This invention relates to a power driven gate assembly for a vertically pivoting gate.
Generally, openings in enclosed areas have gates for controlling ingress and egress via walkways and roadways. The most common gate style is the swinging gate, but, although swinging gates are satisfactory for walkways, their use becomes more cumbersome as they increase in size, such as for roadways. Conventional roadway gates have a number of drawbacks. For example, the weight of roadway gates presents a problem in the provision of adequate hinges and may make the gate difficult to operate. In an attempt to solve these problems, pairs of gates meeting at the center sometimes are utilized.
Another problem with roadway gates is the need for getting out of a vehicle to open the gate, driving the vehicle through, and getting out of the vehicle again to close the gate. For this reason, other proposals for power operated roadway gates have been made, including gate assemblies having overhead frameworks into which the gates are raised. Such gate assemblies of necessity have limited overhead clearance and are unsightly because of the overhead structural elements.
Many of the drawbacks of the gate assemblies just discussed are overcome by power operated gates which pivot so that they stand vertically on end when opened. One such gate, which is the subject of U.S. Pat. No. 3,839,826, utilizes a combination of a tension spring and a torsion spring to assist the power drive mechanism, whereby the tension spring urges the gate from the closed position toward the open position and the torsion spring acts in the opposite direction.
Although this vertically pivoting power driven gate construction offers advantages over swinging gates, particularly in snowy climates, it has certain shortcomings. The drive motor has to be of considerable size because of its location adjacent the pivot point of the gate. Also, the use of the combination of the torsion spring and the tension spring makes the design somewhat complicated and increases its cost. These shortcomings were avoided in the gate assembly disclosed in U.S. Pat. No. 4,470,221, which can be operated with a conventional power source, such as a common garage door opening unit, and can be operated manually if desired using only a minimum of effort. Furthermore, the gate assembly of U.S. Pat. No. 4,470,221 employs an arcuate fulcrum for each tension spring in order to tension the springs as the gate approaches its open position and thereby eliminate the need for a separate spring to perform that function. However, this arrangement tends to place a large torque on the ends of the springs. In addition, known vertically pivoting gates rely on switches in the drive motors to stop the gate in its closed and open positions. These switches, which are usually in the form of knurled knobs, may and do travel from their initial settings, thereby allowing the barrier to open or close beyond its intended limit. As a result, the movement of the gate can be limited by structural members of the gate assembly before the switches shut off current to the motor. Therefore, the motors can overload and burn out.
When the gate pivots past vertical, a component of the weight of the gate acts against the start of the pivoting movement of the gate back toward the closed position and thereby increases the load on the motor. Since the issuance of U.S. Pat. No. 4,470,221, there has been an increased demand for gate assemblies to close even wider openings in enclosures, thereby calling for even longer and heavier gates or barriers. Such great lengths tend to place an excessive load on the pivot shafts and brackets of vertical pivoting the assemblies and to render the gates unstable as they move between their horizonal, closed positions and their vertical, open positions. The increased weight of the longer gates renders the spring arrangements of the previous gate assemblies marginal or totally inadequate in assisting the motor drives.
In the parent application, Ser. No. 001,847, a spring mounting arrangement allows the tension of the motor-assisting springs to be adjusted more easily and additional springs to be mounted for greater motor assistance. Furthermore, a stop member provided in a gate support frame not only supports the gate at precisely 90.degree. to the horizontal when the gate is in the open position, but also places all of the springs in tension as the gate approaches its open position in order to help the motor start moving the gate when closing of the gate is desired. Moreover, the stop member tensions the springs without the need for arcuate fulcrums and avoids the large torsional forces which are induced in the ends of the springs in arrangements using arcuate fulcrums. In addition, stabilizer members extend laterally from the support frame, and ball bearings in pillow blocks are provided for receiving the pivot shaft to accommodate the greater bearing forces generated by longer and heavier gates.
Although the gates disclosed in the parent application have performed well, there has been some concern that the metal of the motor-assisting springs might fatigue after a very high number of cycles of opening and closing of the gate due to the fact that the springs directly contact the stop member, bend laterally about the stop member, and slide on the stop member as the gate opens.